1. Field of Invention
The present invention relates to a method of monitoring semiconductor manufacturing process. More particularly, the present invention relates to a method of removing repeating defects that have no effects on yield and provides a better monitoring of true defects.
2. Description of Related Art
In most plants for manufacturing semiconductors, monitoring stations are frequently set up along a production line after a critical processing operation. The purpose of having a monitoring station is to find out as many defects as possible before subsequent processes are conducted. If defects are left unchecked and the manufacturing operations are permitted to continue as usual, ultimate yield of the product may be severely affected.
For example, in a photomask fabrication process, abnormal patterns are sometimes formed on the photomask. In general, such abnormal mask may be difficult to discover. However, if the abnormal pattern is transferred to a wafer in a subsequent photolithographic process, defects are formed on the wafer. In particular, if a step and repeat exposure technique is used to transfer mask pattern, defects will repeatedly appear in a wafer. These defects are often referred to as repeating defects.
Sometimes, such repeating defects have effects on the yield of a given product. However, a conventional monitoring station will regard the repeating defects as defects in general regardless of the repetitive nature. Hence, the probability of finding out true defects is compromised. This is because most monitoring stations operate by sampling out a portion of the defects to perform an analysis. When repeating defects that have no effect on yield are included in the sample, the monitoring station is less likely to pick up true defects that might affect the yield. Ultimately, effectiveness of the monitoring station is reduced.
Furthermore, if a wafer contains repeating defects, the chance of finding new repeating defects from the wafer is greatly diminished. The new repeating defects on the wafer may appear as a result from problems in a manufacturing station or an abnormal change in the surrounding environment. Anyway, if the defects are not found in time to make necessary re-adjustment or repair to the machines, these defects may be carried forward down the production line leading to a severe loss in production time and yield.
Accordingly, one object of the present invention is to provide a method for deleting repeating defects that have no effect on product yield so that the probability of finding true defects that have an effect on product yield is increased.
A second object of this invention is to provide a method for deleting repeating defects that have no effect on product yield so that any new repeating defects on a wafer can be found more readily.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for deleting repeating defects that have no effect on the product yield of wafer. A wafer having a plurality of dies thereon is provided. A first scanning operation is conducted to find out if there are any repeating defects. The repeating defects include any abnormal pattern due to a transfer from a photomask during a photolithographic process. If no repeating defects are found on the wafer in the first scanning operation, the first scanning data is immediately conducted to find any defects on the wafer that truly affects the ultimate product yield. However, if repeating defects are found, the repeating defects are assessed to determine if such defects might affect the yield. The effect of the repeating defects on yield is assessed through a testing operation. If the repeating defects are found to affect subsequent yield, the photomask used in the previous photolithographic process must berejected. On the other hand, if the repeating defects have no effect on the yield, the area on the wafer containing the repeating defects is marked out as xe2x80x9cdon""t carexe2x80x9d region. A second scanning operation is next carried out scanning the regions outside the xe2x80x9cdon""t carexe2x80x9d region to find out other true defects on the wafer.
In this invention, repeating defects that do not affect yield are deleted. Hence, the probability of finding true defects from a wafer is increased. Moreover, by deleting the repeating defects that result from an abnormality in the photomask and do not have any effect on yield, new repeating defects can be easily found. In addition, each marked-out xe2x80x9cdon""t carexe2x80x9d region typically occupies only about {fraction (1/250000)}th of the area of each die. Therefore, the deleting process will hardly compromise the defect-monitoring capacity of the monitoring station.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.